Field of the Invention
The invention relates to a device for producing purified oxygen.
It relates more specifically to a device for producing purified oxygen by the oxygen production process known as PSA (pressure swing adsorption) which consists in separating the nitrogen molecules contained in the air by passing the air into a column or bed containing a molecular sieve, usually of zeolite type, which is a material having the ability to adsorb the nitrogen molecules, by varying the pressure in an adsorption/desorption cycle.
Description of the Related Art
Although being able to be designed with a single bed, this type of device often comprises two beds that work alternately in adsorption/desorption making it possible to produce, in each cycle, a certain volume of oxygen with a concentration of between 90% and 96%, the other constituents being mainly argon and residues of nitrogen.
Usually, the phases of a PSA cycle are pressurization/production/equalization/depressurization/regeneration.
A second stage may be added to such a device in order to obtain a higher purity of oxygen. Its role is to separate the mixture of oxygen, argon, nitrogen residues and several inert gases in order to extract therefrom oxygen having a high purity that may reach 99.5%.
Also operating according to the PSA process, the second stage comprises one or two beds of molecular sieves, for example carbon molecular sieves, which have the property of adsorbing oxygen. The operation consists in passing the gas mixture into the bed and venting to the atmosphere the portion of the as not adsorbed, namely essentially argon and residues of nitrogen.
Such a device is described, in patent document U.S. Pat. No. 5,137,549.
The two-stage oxygen concentrator that is described therein comprises a first separation stage that separates nitrogen, carbon dioxide, and water vapor from the air. The mixture of oxygen and argon produced by this first stage is injected through a feed valve into a second separation stage which comprises two beds of oxygen adsorption material, a purge for discharging the separated argon, this purge being equipped with a purge valve, and a circuit for injecting a portion of the purified oxygen produced, into the feed of a mixture of oxygen and argon at the feed valve.
The control of the purge valve is carried out in a staggered and alternate manner with respect to the control of the feed valve which itself is carried out at the same time as a transfer valve which is opened or closed in order to connect the two beds in series.
Furthermore, this type of two-stage device for producing purified oxygen is intended to produce a highly purified oxygen and these devices are constructed with fixed parameters defined at the design stage.
By way of example, if a first stage can produce oxygen purified to 93% or 95% with a flow rate of the order of 10 m3/h, a second stage may produce oxygen purified to 99%±0.2% with a flow rate of the order of 5 m3/h.
However, it turns out that the requirement of the users may differ as regards the degree of purity of the oxygen and/or as regards the production flow rate of purified oxygen produced. No solution is currently provided in order to meet these different specific needs or in order to optimize the relative performances of purity of the oxygen produced and of production flow rate, during operation.